The present invention relates to a method for producing a polymer electrolyte membrane and a fuel cell.
A fuel cell includes an electrolyte and a pair of electrodes. In the fuel cell, a hydrogen gas is supplied to one of the electrodes, and an oxidizing agent such as an oxygen gas is supplied to the other electrode, thereby converting chemical energy involved in the oxidation of the fuel into electric energy. The electrolyte permeates hydrogen ions but does not permeate reactive gases such as the hydrogen gas and the oxygen gas.
As the electrolyte for the fuel cell, a solid such as a polymer electrolyte membrane and a liquid such as phosphoric acid are used. Recently, a polymer electrolyte membrane has preferably been used as the electrolyte for the fuel cell, and particularly perfluorosulfonic acid polymer has been receiving attention. Typically, the perfluorosulfonic acid polymer has a framework of perfluorocarbon such as a copolymer of tetrafluoroethylene and trifluorovinyl and a side chain being bonded thereto and having a sulfonic acid group such as a side chain that a sulfonic acid group is bonded to perfluoroalkylene group. The sulfonic acid group releases a hydrogen ion to produce an anion, and therefore conducts proton.
Typically, the polymer electrolyte membrane has been produced with melt extrusion technology. Since, perfluoropolymer does not dissolve in a solvent, a special process such as melt extrusion and membrane extension is required to produce a membrane and to control its properties such as a thickness. Therefore, it is desired to provide a convenient process for producing a polymer electrolyte membrane. Moreover, it has always been desired to improve an output of the fuel cell.
Japanese patent application laid open No. 3-106616 teaches a method for producing a tubular body comprising the steps of: coating a raw material on an inner surface of a cylinder having a cylindrical configuration while rotating the cylinder; rotating the cylinder thereby forming a tubular body by a centrifugal force of the rotation; and removing the tubular body from the cylinder. However, the document does not teach a polymer electrolyte membrane for a fuel cell at all.
U.S. Pat. No. 5,561,202 discloses a polymer electrolyte membrane. However, the membrane is cast onto a glass plate and afterwards coagulated.
According to one aspect of the present invention, there is provided a method for producing a polymer electrolyte membrane adapted to a fuel cell, comprising the steps of:
introducing a first liquid medium into a cylinder having an inner surface having a cylindrical configuration, the first liquid medium having at least one percent by weight of a first polymer electrolyte and a first solvent having a boiling point or an azeotropic point ranging from 60 to 220xc2x0 C.; and
rotating the cylinder for evaporating the first solvent by means of a centrifugal force created by such rotation so as to form a first polymer electrolyte membrane having a cylindrical configuration with a substantially uniform thickness on the inner surface of the cylinder.
According to another aspect of the present invention, there is provided a fuel cell comprising:
a polymer electrolyte membrane obtained by cutting off a polymer electrolyte membrane obtained by the aforementioned method; and
a pair of electrodes sandwiching the polymer electrolyte membrane.